Why do I get the Error: Unable to find a bootable option. Press any key to shut down?

I am using the Windows Insider Program and have installed Windows 10 on my Nokia Lumia 625. This morning my phone had the following message on my screen: Error: Unable to find a bootable option. Press any key to shut down.
I have tried soft resetting and hard resetting the phone but the Error message keeps re-appearing and not allowing me to perform either re-set.

There are two things you can try:
1. Try connecting your phone to your PC and launch the Lumia Software Recovery Tool. Select the option that says that your phone won't start up. If your phone gets detected successfully, your PC will begin reinstalling the OS on your phone - this should resolve the issue.

2. If your phone was not successfully detected by your PC, then the only option is to take your phone to a service center and have them repair it. Note that as soon as you mention that you've tried installing the technical preview, any warranty your phone may have could be considered void.

This happened to my L1020 several months ago. PC didn't detect my phone. Took it to a service center. Got it back after 90 days.

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Check the warranty of your phone. In my case, they replaced the "main board" of my L1020 for free, but I had to wait (as mentioned). If your phone is still under warranty, they should also repair your phone without fees.

the real story that worked for 1020, you need another lumia for this process though, on other lumia (working) try to restore as normally with recovery tool, then after downloading of firmware of working lumia, just after tools says "preparing to flash" which means its going to flash mode disconnect the healthy(working lumia) and plug in the lumia that shows "unable to find a bootable option. press any key to shut down " screen. then it should boot to flash mode and flash the firmware files. It worked on my 1020 i was worried.

lol you don't have to replace the whole motherboard, in some rare or worst case if my suggestion didn't worked you gotta try this SUCCESS Lumia 520 WPLock EMMC Error "Unable to Find a Bootable option" - GSM-Forum , the error is caused due to what is called emmc memory(embedded memory) on ur hardware, I repeat its the worst case only and can be 100% fixed using jtag(search for it). But if ur phone is bricked suddenly or due to some making mess in system files or wp internals thing then my solution will work for sure. Yeah, you may find it difficult or may not be succeeded but its worth trying than sitting as it is or looking for other's folk NONSENSE suggestion like take to service center replace motherboard, buy another device, etc. I repeated there is NO need to REPLACE MOTHERBOARD.